- Epithelial stem cells are responsible for the continual regeneration and homeostasis of all self-renewing tissues such as the epidermis, hair follicle, corneal epithelium, and seminiferous epithelium. The applicant originally identified groups of epithelial stem cells in the limbal epithelium of the cornea, and in the bulge region of the outer root sheath of the hair follicle. The long-term goals of this project are to advance our understanding of these epithelial stem cells by identifying genes that are preferentially expressed or unique to stem cell-rich areas such as the bulge. It is hypothesized in this proposal that molecules unique or upregulated in stem cell-rich tissue are responsible for maintaining their stem cell attributes (e.g., slow-cycling and high proliferative potential). Using a PCR-based subtraction hybridization technique, the principal investigator has isolated four partial cDNA clones which appear to be differentially expressed in cultured outer root sheath cells from the bulge. In addition, he created a cell line and a cDNA library from these cells. Screening this library with a candidate clone, he obtained a nearly full-length sequence of a previously undescribed cDNA (B10) that appears to be preferentially expressed in outer root sheath cells. This clone has also been found in testis. The research objective of the proposal is to characterize the expression of this gene and its protein product in epithelial tissues with known populations of stem cells to evaluate its potential as a stem cell marker. Because the hair follicle serves as a model for mesenchymal-epithelial interactions, any insight into the specific molecules elaborated by epithelial stem cells could have broad implications on our understanding of epithelial differentiation and proliferation. Additionally, patients with disorders of proliferating tissues such as alopecia, basal cell carcinoma, chronic wounds, or oligospermia may ultimately benefit from this research.